Right and left side sills of a vehicle are essential elements of a vehicle body frame, as disclosed in Patent Literature 1 below. A side sill disclosed in Patent Literature 1 is reinforced by a reinforcement member extending along an inside of the side sill. The reinforcement member can prevent the side sill from being bent by an impact force applied to a side portion of a vehicle upon impact on the side portion of the vehicle.
Recently, a technique for increasing a rigidity of a vehicle body has been needed. To increase the rigidity of the vehicle body, it may be suggested that rigidities of right and left side sills be increased and rigidities of junctions where rear end portions of the side sills are joined to right and left rear wheelhouses be increased. However, this suggestion is not preferable. This is because the vehicle body may have a complex structure and a heavy weight if the rigidities of the side sills and the rigidities of the junctions are merely increased.
It may also be suggested that the right and left side sills be connected to the right and left rear wheelhouses through right and left connection members. These connection members need to conform to a vehicular body shape. The side sills differ in cross-sectional shape from the rear wheelhouses, therefore, rigidities of the connection members need to be sufficiently increased taking into consideration a structural continuity between the side sills and the rear wheelhouses. It is thus necessary to improve the technique for increasing the rigidity of the vehicle body.